This application is based on Japanese Patent Applications Nos. 2000-111927 and 2000-368339, filed on Apr. 7, 2000 and Dec. 4, 2000, respectively, the contents of which are hereby incorporated by reference.
The present invention relates to an optical or taking lens device. More specifically, the present invention relates to an optical or taking lens device that optically takes in an image of a subject through an optical system and that then outputs the image as an electrical signal by means of an image sensor. For example, a taking lens device that is used as a main component of a digital still camera, a digital video camera, or a camera that is incorporated in, or externally fitted to, a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to an optical or taking lens device provided with a compact, high-zoom- ratio zoom lens system.
Conventionally, the majority of high-zoom-ratio zoom lenses for digital cameras are of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H4-296809). This is because a positive-negative-positive-positive configuration excels in compactness.
On the other hand, as zoom lenses that offer higher zoom ratios are known zoom lenses of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power (for example, Japanese Patent Application Laid-Open No. H5-341189) and zoom lenses of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, a fourth lens unit having a negative optical power, and a fifth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H10-111457).
However, in the zoom lens of a positive-negative-positive-negative configuration proposed in Japanese Patent Application Laid-Open No. H5-341189, mentioned above, the first lens unit is kept stationary during zooming, and therefore this zoom lens is unfit for further improvement for higher performance necessitated by the trend toward higher zoom ratios and smaller image-sensor pixel pitches. On the other hand, in the zoom lens of a positive-negative-positive-negative-positive configuration proposed in Japanese Patent Application Laid-Open No. H10-111457, mentioned above, the first lens unit is moved during zooming, but the individual lens units, in particular the first and second lens units, are given strong optical powers and thus cause large aberrations. This makes it difficult to achieve higher performance necessitated by the trend toward higher zoom ratios and smaller image-sensor pixel pitches. In addition, a configuration including a positive-negative-positive-negative sequence, in which the fourth lens unit is negative, is somewhat inferior in compactness to a positive-negative-positive-positive configuration.
An object of the present invention is to provide a zoom lens configuration that is superior in compactness to a positive-negative-positive-positive configuration but that still offers satisfactory performance. In particular, an object of this invention is to provide an optical or taking lens device provided with a high-zoom-ratio zoom lens system that offers a zoom ratio of about 7xc3x97 to 10xc3x97 and an f-number of about 2.5 to 4, that offers such high performance that it can be used as an optical system for use with a leading-edge image sensor with a very small pixel pitch, and that excels in compactness.
To achieve the above object, according to one aspect of the present invention, an optical or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises at least, from the object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power. Here, the following conditional formula is fulfilled:
1.1 less than f1/fT less than 2.5
where
f1 represents the focal length of the first lens unit; and
fT represents the focal length of the entire optical system at the telephoto end.
According to another aspect of the present invention, an optical, or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units which achieves zooming by varying the unit-to-unit distances; and an image sensor for converting an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power. The first lens unit is moved as zooming is performed. Here, the following conditional formula is fulfilled:
0.3 less than D34W/D34T less than 2.5
where
D34W represents the aerial distance between the third lens unit and the fourth lens unit at the wide-angle end; and
D34T represents the aerial distance between the third lens unit and the fourth lens unit at the telephoto end.